Systems and Methods for Encoding Alternative Streams of Video for Playback on Playback Devices Having Predetermined Display Aspect Ratios and Network Connection Maximum Data Rates

ABSTRACT

Systems and methods for adaptive bitrate streaming of alternative streams of video encoded at resolution and sample aspect ratio combinations and maximum bitrates in accordance with embodiments of the invention are disclosed. In one embodiment of the invention, a source encoder configured to encode a source video stream as a plurality of alternative streams of video for playback on a playback device includes a processor configured to receive multimedia content including source video data having a primary resolution, a primary sample aspect ratio, and a primary frame rate and to encode the source video data as alternative streams of video, where the resolution and sample aspect ratio of at least one of the alternative streams of video are selected to have an aspect ratio that is the same as a predetermined display aspect ratio and at least one of the alternative streams is encoded at a maximum bitrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

The current application is a continuation of U.S. patent applicationSer. No. 14/464,146 filed Aug. 20, 2014 which is a continuation of U.S.patent application Ser. No. 13/432,521 filed Mar. 28, 2012 which issuedon Aug. 26, 2014 as U.S. Pat. No. 8,818,171 which claimed priority toU.S. Provisional Patent Application No. 61/529,204, filed Aug. 30, 2011,the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the delivery of multimedia content andmore specifically streaming video content encoded at a variety ofrecommended maximum bitrates optimized for a variety of scaled displayresolutions and network connection maximum data rates of playbackdevices receiving the streams.

BACKGROUND OF THE INVENTION

The term streaming media describes the playback of media on a playbackdevice, where the media is stored on a server and continuously sent tothe playback device over a network during playback. Typically, theplayback device stores a sufficient quantity of media in a buffer at anygiven time during playback to prevent disruption of playback due to theplayback device completing playback of all the buffered media prior toreceipt of the next portion of media. Adaptive bit rate streaming oradaptive streaming involves detecting the present streaming conditions(e.g. the user's network bandwidth and CPU capacity) in real time andadjusting the quality of the streamed media accordingly.

In adaptive streaming systems, the source media is typically stored on amedia server as a top level index file pointing to a number of alternatestreams that contain the actual video and audio data. Each stream istypically stored in one or more container files. Different adaptivestreaming solutions typically utilize different index and mediacontainers. The Matroska container is a media container developed as anopen standard project by the Matroska non-profit organization ofAussonne, France. The Matroska container is based upon Extensible BinaryMeta Language (EBML), which is a binary derivative of the ExtensibleMarkup Language (XML). Decoding of the Matroska container is supportedby many consumer electronics (CE) devices. The DivX Plus file formatdeveloped by DivX, LLC of San Diego, Calif. utilizes an extension of theMatroska container format, including elements that are not specifiedwithin the Matroska format.

SUMMARY OF THE INVENTION

Systems and methods for adaptive bitrate streaming of alternativestreams of video encoded at resolution and sample aspect ratiocombinations and maximum bitrates corresponding to the display aspectratios and network connection maximum data rates of playback devicesreceiving the streams in accordance with embodiments of the inventionare disclosed. In one embodiment of the invention, a source encoderconfigured to encode a source video stream as a plurality of alternativestreams of video for playback on a playback device includes a processorconfigured by an encoding application to receive multimedia content,where the multimedia content includes source video data having a primaryresolution, a primary sample aspect ratio, and a primary frame rate andto encode the source video data as a set of alternative streams ofvideo, where the resolution and sample aspect ratio of at least one ofthe alternative streams of video are selected to have an aspect ratiothat is the same as a predetermined display aspect ratio and at leastone of the alternative streams is encoded at a maximum bitratecorresponding to a predetermined network connection maximum data rate.

In another embodiment of the invention, the encoding application furtherconfigures the processor to select a resolution, sample aspect ratio,and frame rate for one of the alternative streams, determine a maximumbitrate threshold beyond which higher video quality can be achievedusing a higher resolution than the selected resolution at the selectedframe rate, and encode the source video stream at the predeterminednetwork connection maximum data rate, when the predetermined networkconnection maximum data rate is less than the maximum bitrate threshold.

In an additional embodiment of the invention, the source encoderincludes an encoding profile, where the encoding profile specifies aplurality of maximum bitrates including a maximum bitrate correspondingto the predetermined network connection maximum data rate, wherein theencoding application further configures the processor to select aresolution, sample aspect ratio and frame rate for each alternativestream, determine a maximum bitrate threshold beyond which higher videoquality can be achieved using a higher resolution than the selectedresolution at the selected frame rate of each alternative stream, selecta maximum bitrate from the profile for each alternative stream, wherethe selected maximum bitrate is the highest maximum bitrate specified inthe profile that is less than the maximum bitrate threshold determinedfor the alternative stream, and generate each alternative stream byencoding the source video stream at the selected maximum bitrate,selected resolution, sample aspect ratio and frame rate.

In yet another additional embodiment of the invention, the encodingapplication further configures the processor to determine a maximumbitrate threshold beyond which higher video quality can be achievedusing a higher resolution than the selected resolution at the selectedframe rate by configuring the processor to determine the maximum bitratethreshold using an adjusted number of macroblocks per second determinedbased upon the selected resolution, and frame rate.

In still another embodiment of the invention, the encoding applicationconfigures the microprocessor to determine the adjusted number ofmacroblocks per second (AMBPS) as follows:

AMBPS=((width*height*FPS)/256)*AdjustmentFactor(FPS),

where width and height are the width and height of the encodingresolution, FPS is the frame rate per second for the video data, andAdjustmentFactor(FPS) is a predetermined value based on the FPS of thevideo data.

In yet still another additional embodiment of the invention, theadjustment factor is selected from the group including:

an AdjustmentFactor(FPS)=1, where FPS=29.97,

an AdjustmentFactor(FPS)=1.1333, where FPS=25, and

an AdjustmentFactor(FPS)=1.1606, where FPS=23.976.

In yet another embodiment of the invention, the encoding applicationconfigures the processor to determine the adjustment factor isdetermined as follows:

AdjustmentFactor(FPS)=1+((MaxFPS−FPS)/(MaxFPS*1.25))

where MaxFPS is Ceiling (FPS/30)*30.

Still another embodiment of the invention includes encoding a sourcevideo stream as a plurality of alternative streams of video for playbackon a playback device, including receiving multimedia content using asource encoder, where the multimedia content comprises source video datahaving a primary resolution, a primary sample aspect ratio, and aprimary frame rate and encoding the source video data using the sourceencoder as a set of alternative streams of video, where encoding thesource video includes selecting the resolution and sample aspect ratioof at least one of the alternative streams of video to have an aspectratio that is the same as the predetermined display aspect ratio andencoding at least one of the alternative streams at a maximum bitratecorresponding to the predetermined network connection maximum data rate.

In yet another additional embodiment of the invention, encoding a sourcevideo stream as a plurality of alternative streams of video for playbackon a playback device further includes selecting a resolution, sampleaspect ratio, and frame rate for one of the alternative streams,determining a maximum bitrate threshold beyond which higher videoquality can be achieved using a higher resolution than the selectedresolution at the selected frame rate using the source encoder, andencoding the source video stream at the predetermined network connectionmaximum data rate using the source encoder, when the predeterminednetwork connection maximum data rate is less than the maximum bitratethreshold.

In still another additional embodiment of the invention, encoding asource video stream as a plurality of alternative streams of video forplayback on a playback device further includes retrieving an encodingprofile using the source encoder, where the encoding profile specifies aplurality of maximum bitrates including a maximum bitrate correspondingto the predetermined network connection maximum data rate, selecting aresolution, sample aspect ratio and frame rate for each alternativestream, determining a maximum bitrate threshold beyond which highervideo quality can be achieved using a higher resolution than theselected resolution at the selected frame rate of each alternativestream using the source encoder, selecting a maximum bitrate from theprofile for each alternative stream using the source encoder, where theselected maximum bitrate is the highest maximum bitrate specified in theprofile that is less than the maximum bitrate threshold determined forthe alternative stream, and generating each alternative stream using thesource encoder by encoding the source video stream at the selectedmaximum bitrate, selected resolution, sample aspect ratio and framerate.

In still yet another additional embodiment of the invention, determiningthe maximum bitrate threshold using an adjusted number of macroblocksper second determined based upon the selected resolution and frame rate.

In still another embodiment of the invention, determining the adjustednumber of macroblocks per second (AMBPS) as follows:

AMBPS=((width*height*FPS)/256)*AdjustmentFactor(FPS),

where width and height are the width and height of the encodingresolution, FPS is the frame rate per second for the video data, andAdjustmentFactor(FPS) is a predetermined value based on the FPS of thevideo data.

In yet another additional embodiment of the invention, the adjustmentfactor is selected from the group comprising:

an AdjustmentFactor(FPS)=1, where FPS=29.97;

an AdjustmentFactor(FPS)=1.1333, where FPS=25; and

an AdjustmentFactor(FPS)=1.1606, where FPS=23.976.

In still yet another embodiment of the invention, the encodingapplication configures the processor to determine the adjustment factoris determined as follows:

AdjustmentFactor(FPS)=1+((MaxFPS−FPS)/(MaxFPS*1.25))

where MaxFPS is Ceiling (FPS/30)*30.

Still another embodiment of the invention includes a playback deviceconfigured to playback content on a display having a display aspectratio, including a processor configured to communicate with a memory,where the memory contains a client application, wherein the clientapplication configures the processor to connect to a contentdistribution system via a network connection, where the networkconnection has a predetermined maximum likely data rate, obtain an indexfile from the content distribution system, where the index filedescribes a plurality of alternative video streams, where at least oneof the alternative video streams has the same aspect ratio as thedisplay aspect ratio and is encoded at a maximum bitrate correspondingto the predetermined maximum likely data rate, and request a portion ofat least one of the alternative streams using the index file.

Still another embodiment of the invention includes playing back content,including connecting to a content distribution system using a playbackdevice via a network connection, where the network connection has apredetermined maximum likely data rate, obtaining an index file from thecontent distribution system using the playback device, where the indexfile describes a plurality of alternative video streams, where at leastone of the alternative video streams has the same aspect ratio as thedisplay aspect ratio and is encoded at a maximum bitrate correspondingto the predetermined maximum likely data rate, requesting a portion ofat least one of the alternative streams using the playback device andthe index file, and playing back the requested portions of the at leastone alternative streams using the playback device.

Still another embodiment of the invention includes a machine readablemedium containing processor instructions, where execution of theinstructions by a processor causes the processor to perform a processincluding retrieving an encoding profile, where the encoding profilespecifies a plurality of maximum bitrates including a maximum bitratecorresponding to the predetermined network connection maximum data rate,and a set of predetermined minimum adjusted macroblocks per second(MAMBPS) corresponding to each one of the maximum bitrates, selecting anencoding bitrate according to the corresponding value of the MAMBPS,selecting a resolution, sample aspect ratio and frame rate for eachalternative stream, determining a maximum bitrate threshold beyond whichhigher video quality can be achieved using a higher resolution than theselected resolution at the selected frame rate of each alternativestream, selecting a maximum bitrate from the profile for eachalternative stream, where the selected maximum bitrate corresponds tothe MAMBPS that generates the highest positive difference between theAMBPS and the MAMBPS for the alternative stream, and generating eachalternative stream by encoding the source video stream at the selectedmaximum bitrate, selected resolution, sample aspect ratio and framerate.

In yet another additional embodiment of the invention, if the highestpositive number that corresponds to the difference between the AMBPS andMAMBPS is zero, the resolution corresponding to the AMBPS is not allowedby the encoding profile.

Still another embodiment of the invention includes a machine readablemedium containing processor instructions, where execution of theinstructions by a processor causes the processor to perform a processincluding connecting to a content distribution system via a networkconnection, where the network connection has a predetermined maximumlikely data rate, obtaining an index file from the content distributionsystem, where the index file describes a plurality of alternative videostreams, where at least one of the alternative video streams has thesame aspect ratio as the display aspect ratio and is encoded at amaximum bitrate corresponding to the predetermined maximum likely datarate, requesting a portion of at least one of the alternative streamsusing the index file, and playing back the requested portions of the atleast one alternative streams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a network diagram of an adaptive bitrate streaming systemconfigured to stream video encoded at recommended maximum bitrates inaccordance with an embodiment of the invention.

FIG. 2 is a flow chart illustrating a process for determining arecommended bitrate in accordance with an embodiment of the invention.

FIG. 3 is a flow chart illustrating a process for determining anadjustment factor in accordance with an embodiment of the invention.

FIG. 4 conceptually illustrates a source encoder configured to encodevideo data utilizing different video bitrates in accordance with anembodiment of the invention.

FIG. 5 is a table illustrating an example of a profile with definedmaximum bitrates in accordance with an embodiment of the invention.

FIG. 6 is a table illustrating an example of a set of maximum bitratesand corresponding encoding and decoding minimum adjusted macroblocks persecond in accordance with an embodiment of the invention.

DETAILED DISCLOSURE OF THE INVENTION

Turning now to the drawings, systems and methods for adaptive bitratestreaming of alternative streams of video encoded at resolution andsample aspect ratio combinations and maximum bitrates corresponding tothe display aspect ratios and network connection maximum data rates ofplayback devices receiving the streams in accordance with embodiments ofthe invention are illustrated. Adaptive bitrate streaming systems canstream alternative streams of video data encoded at maximum bitrates. Inorder to provide the highest quality video experience independent of thenetwork data rate, the adaptive bitrate streaming systems switch betweenthe available streams of video data throughout the delivery of the videodata according to a variety of factors, including, but not limited to,the available network data rate and video decoder performance. Systemsand methods for switching between video streams during playback aredisclosed in U.S. patent application Ser. No. 13/221,682 entitled“Systems and Methods for Adaptive Bitrate Streaming of Media Stored inMatroska Container Files Using Hypertext Transfer Protocol” to Branesset al., filed Aug. 30, 2011, the disclosure of which is incorporated byreference herein in its entirety.

The data rate experienced by a playback device during adaptive bitratestreaming typically depends upon the technologies that the playbackdevice utilizes to connect to the Internet and the Internet ServiceProvider that provides the Internet connection. Playback devices thatutilize the same Internet Service Provider often experience similarmaximum data rates that can deteriorate from time to time based uponnetwork congestion and/or the processing load of the playback device. Inadaptive bitrate streaming systems, the highest quality video that aplayback device can receive is typically video encoded at a maximumbitrate equal to the maximum data rate of the network connection of aplayback device. Where the video stream is transmitted in conjunctionwith other streams such as (but not limited to) an audio stream, asubtitle stream and/or a metadata stream, then the effective maximumdata rate available for the video stream is equal to the maximum datarate, less the maximum data rates of each of the other streams alongwith a reserved data rate value that is greater than or equal to zero.An adaptive bitrate streaming system designed to deliver a video streamvia the Internet to a variety of playback devices utilizing differentInternet Service Providers can identify a set of effective maximum datarates corresponding to the effective maximum data rates likely to beexperienced by each of the playback devices. For each effective maximumdata rate in the set, the adaptive bitrate streaming system can thenencode an alternative video stream having a maximum bitratecorresponding to the effective maximum data rate. In this way, aplayback device is likely to be able to stream video encoded at thehighest quality that can be supported by the playback device's networkconnection. In the event that streaming conditions deteriorate, theadaptive bitrate streaming system can stream video encoded at a lowermaximum bitrate. Under normal streaming conditions, however, a videostream is available that is encoded to fully utilize the availablenetwork connection.

Due to standardization, video sources typically have a display aspectratio selected from one of a number of common display aspect ratios. Asis described in U.S. patent application Ser. No. 13/430,032, theperformance of an adaptive bitrate streaming system can be enhanced byencoding each of the alternative streams using resolutions and sampleaspect ratios that result in a common aspect ratio across thealternative streams corresponding to the display aspect ratio of theoriginal video source. When a set of alternative video streams isencoded with resolutions and sample aspect ratios that result in anaspect ratio corresponding to the display aspect ratio of the originalsource, then each pixel of encoded video can be scaled to an integernumber of pixels on the display and the playback device can smoothlytransition between the streams without the need to resample the streamsor add padding rows and/or columns to the decoded video to fit it to thedisplay resolution.

U.S. patent application Ser. No. 13/430,032 also notes that the videoquality of a stream encoded with a specific resolution and sample aspectratio typically does not improve appreciably beyond a specific maximumbitrate threshold. Beyond that threshold, increasing the resolution ofthe encoded video can increase video quality.

Adaptive bitrate steaming systems in accordance with embodiments of theinvention select a set of resolutions and sample aspect ratiocombinations that have an aspect ratio corresponding to a specificdisplay aspect ratio and encode an alternative stream at each resolutionand sampling aspect ratio combination. The maximum bitrate used toencode each alternative stream is selected based upon a set ofpredetermined maximum bitrates corresponding to the maximum effectivedata rates of the network connections of the playback devices within theadaptive bitrate streaming system. The specific maximum bitrate selectedfor a specific resolution and sample aspect ratio combination may bedetermined based upon estimating the maximum bitrate threshold for thespecific resolution and sample aspect ratio combination beyond whichvideo quality does not appreciably improve and then identifying amaximum bitrate from the set of predetermined maximum bitrates that isthe closest maximum bitrate that is less than the threshold. As isdiscussed further below, the maximum bitrate threshold for a specificresolution and sample aspect ratio combination typically depends uponthe frame rate of the video.

By encoding at least one of the alternative streams of video provided byan adaptive bitrate streaming system in accordance with embodiments ofthe invention using a resolution and sample aspect ratio combination andmaximum bitrates corresponding to the aspect ratio of the source contentand maximum effective data rate of a playback device, the playbackdevice can stream video encoded to provide the highest quality of videoplayback capable of being supported by the playback device given itsnetwork connection. By encoding lower maximum bitrate streams usingresolution and sample aspect ratio combinations having the same aspectratio as the source content's aspect ratio, the adaptive bitratestreaming system can smoothly transition to streams encoded at lowermaximum bitrates when streaming conditions deteriorate. Adaptive bitratestreaming systems configured to stream alternative streams of videoencoded at resolution and sample aspect ratio combinations and maximumbitrates corresponding to the display aspect ratios of the sourcecontent and network connection maximum effective data rates of theplayback devices within the adaptive bitrate streaming system inaccordance with embodiments of the invention are discussed furtherbelow.

System Overview

An adaptive bitrate streaming system in accordance with an embodiment ofthe invention is illustrated in FIG. 1. The adaptive bitrate streamingsystem 100 includes a source encoder 106 configured to encode sourcevideo as a number of alternative video streams at resolution and sampleaspect ratio combinations and maximum bitrates corresponding to thedisplay aspect ratios of the source content and network connectionmaximum effective data rates of the playback devices within the adaptivebitrate streaming system. In the illustrated embodiment, the sourceencoder is a server. In other embodiments, the source encoder can be anyprocessing device including a processor and sufficient resources toperform the transcoding of source media (including but not limited tovideo, audio, and/or subtitles). The source encoding server 106typically generates a top level index to a plurality of container filescontaining the streams, at least a plurality of which are alternativestreams. Alternative streams are streams that encode the same mediacontent in different ways. In many instances, alternative streams encodemedia content (such as but not limited to video) at different resolutionand sample aspect ratio combinations and different maximum bitrates. Ina number of embodiments, the alternative streams are encoded atdifferent frame rates. In a number of embodiments, alternative videostreams form sets of alternative video streams encoded with the sameaspect ratio corresponding to the display aspect ratio of a set ofsource content. In many embodiments, the maximum bitrates used in theencoding of each alternative stream in a set of alternative streams isdetermined based upon the maximum effective data rate typicallyexperienced by different sets of playback devices based upon factorsincluding (but not limited to) the technology and Internet ServiceProviders the playback devices use to connect to the Internet. The toplevel index file and the container files are uploaded to a contentdistribution server 104. Although the source encoding server 106 isdescribed above as generating the top level index file, in manyembodiments the top level index file is dynamically generated inresponse to a request for a specific piece of content by a playbackdevice.

In the illustrated embodiment, playback devices include personalcomputers 110, CE players 108, and mobile phones 112. In otherembodiments, playback devices can include consumer electronics devicessuch as DVD players, Blu-ray players, televisions, set top boxes, videogame consoles, tablets, and other devices that are capable of connectingto a server via HTTP and playing back encoded media. In the illustratedembodiment, a variety of playback devices use HTTP or anotherappropriate stateless protocol to request portions of a top level indexfile and the container files via a network 102 such as the Internet.Prior to a playback device performing adaptive bitrate streaming usingportions of media from alternative streams contained within thecontainer files, a bandwidth probe can be performed by the playbackdevice to determine available bandwidth. Once the bandwidth probe hasbeen completed, the playback device can utilize data within the toplevel index including (but not limited to) the maximum bitrate of eachof the available streams to determine the initial streams from which tocommence requesting portions of encoded media as part of an adaptivestreaming process.

Once playback of content from the initial set of streams commences, theplayback device utilizes the top level index to perform adaptive bitratestreaming of the content in response to changes in streaming conditions.In many adaptive bitrate streaming systems, the playback device canprogress through a series of operational phases in which the playbackdevice responds differently in each phase to changes in the streamingconditions. In a number of embodiments, stability in streamingconditions or improving streaming conditions can result in a transitionto a phase in which the playback device assumes stable operatingconditions, buffers more content, and is less responsive to fluctuationsin streaming conditions. In many embodiments, a deterioration instreaming conditions results in a stream switch to a set of streamsutilizing less bandwidth and resulting in the playback devicetransitioning to a phase in which the playback device assumes unstableoperating conditions, buffers less content, and responds rapidly tovariations in streaming conditions.

In the illustrated embodiment, the adaptive bitrate streaming systemincludes one or more source encoders capable of encoding a stream ofvideo content into alternative streams of video content encoded atresolution and sample aspect ratio combinations and maximum bitratescorresponding to the display aspect ratios of the source content andnetwork connection maximum effective data rates of the playback deviceswithin the adaptive bitrate streaming system. In many embodiments, thesource encoder can be implemented using any device capable of encodingstreams of multimedia, where the streams are encoded at differentresolutions, sampling rates and/or maximum bitrates. The basicarchitecture of an adaptive streaming system source encoder inaccordance with an embodiment of the invention is illustrated in FIG. 4.The adaptive bitrate streaming system 400 includes a processor 410 incommunication with non-volatile memory 430 and volatile memory 420. Inthe illustrated embodiment, the volatile memory includes a sourceencoder 422 and alternative streams of video data 424. Although aspecific architecture is illustrated in FIG. 4, any of a variety ofarchitectures can be utilized to implement source encoders capable ofencoding a stream of video content into alternative streams of videocontent encoded at resolution and sample aspect ratio combinations andmaximum bitrates corresponding to the display aspect ratios of thesource content and network connection maximum effective data rates ofthe playback devices within an adaptive bitrate streaming system inaccordance with embodiments of the invention. In many embodiments, thevariety of architectures include architectures where the application islocated on disk or some other form of storage and is loaded intovolatile memory at runtime. Furthermore, any of a variety of systemarchitectures including (but not limited) to the system architectureillustrated in FIG. 1 can be utilized to perform video delivery inaccordance with embodiments of the invention. Systems and methods fordetermining resolution and sample aspect ratios for alternative videostreams and the maximum bitrates at which to encode the alternativevideo streams in accordance with embodiments of the invention arediscussed further below.

Determining Maximum Bitrates

Adaptive bitrate streaming systems in accordance with embodiments of theinvention select the maximum bitrate at which to encode a video streamhaving a given resolution and sample aspect ratio based upon the bitratethreshold beyond which video quality no longer appreciably improves andthe maximum effective bitrates likely to be experienced by differentclasses of playback device within the adaptive bitrate streaming system.The set of maximum data rates for different classes of playback devicestypically depends upon the requirements of a specific application. Oncethe set of maximum data rates is determined, the maximum bitrate atwhich to encode a video stream having a specific resolution, sampleaspect ratio and frame rate can be determined by determining the bitratethreshold beyond which video quality no longer appreciably improves andthen selecting the maximum data rate that is closest to and less thanthe bitrate threshold. As noted above, video quality at a given maximumbitrate can be higher at a lower resolution. Beyond a maximum bitratethreshold, however, improvements in video quality at a specificresolution diminish with increases in maximum bitrate. Typically,increasing resolution is the best way to achieve significantimprovements in video quality beyond the threshold. The bitratethreshold is largely qualitative and can be defined in any of a varietyof ways. Bitrate thresholds can be defined that generally apply to allvideo streams encoded at a given resolution, sample aspect ratio andframe rate irrespective of the content of the video. In manyembodiments, maximum bitrate thresholds are in terms of a maximum numberof macroblocks per second or as a maximum bitrate.

A generalized process for selecting maximum bitrates at which to encodea plurality of alternative streams using a profile of maximum bitratescorresponding to typical network connection data rates within anadaptive bitrate streaming system in accordance with an embodiment ofthe invention is illustrated in FIG. 2. The process 200 commences byselecting (210) resolution and sample aspect ratio combinations for thealternative streams. In a number of embodiments, processes similar tothose outlined in U.S. patent application Ser. No. 13/430,032 areutilized to select resolution and sample aspect ratio combinations thathave the same aspect ratio. The adjusted macroblocks per second (AMBPS)is then calculated (212) for each encoding resolution. In manyembodiments of the invention, the following formula may be utilized tocalculate the AMBPS for an encoding resolution:

AMBPS=((width*height*FPS)/256)*AdjustmentFactor(FPS),

where width and height are the width and height of the encodingresolution,

-   -   fps is the frame rate per second for the video data, and    -   AdjustmentFactor(FPS) is a predetermined value based on the FPS        of the video data.

In several embodiments, the following adjustment factors are used forthe following common frame rates:

FPS=29.97,AdjustmentFactor(FPS)=1;

FPS=25,AdjustmentFactor(FPS)=1.1333; and

FPS=23.976,AdjustmentFactor(FPS)=1.1606.

In many embodiments, the following general formula may be applied todetermine the adjustment factor for any variety of frame rates,including when the frame rate of the video data is greater than 30 FPS:

AdjustmentFactor(FPS)=1+((MaxFPS−FPS)/(MaxFPS*1.25)),

where FPS is the FPS of the video data and MaxFPS=Ceiling (FPS/30)*30.

Once the AMBPS is calculated, it is compared to the set of minimumadjusted macroblocks per second (MAMBPS) that are associated withmaximum bitrates determined based upon the effective maximum data ratesthat are likely to be experienced by playback devices within theadaptive bitrate streaming system to determine the differences (214)between the calculated AMBPS and the recommended MAMBPS. An example 600of a set of MAMBPS in accordance with an embodiment of the invention isillustrated in FIG. 6. An example 500 of a set of predetermined bitratesin accordance with an embodiment of the invention is shown in FIG. 5,and the association of MAMBPS and those bitrates in FIG. 6. Once thedifferences are calculated, in many embodiments the differences aresorted (216). The smallest positive difference between the calculatedAMBPS and the MAMBPS is selected (218) (i.e. the highest value of theminimum adjusted macroblocks per second value that is closest to andless than the AMBPS). The bitrate corresponding to the smallest positivedifference is selected (220) as the maximum bitrate for the encoding ofthe alternative video stream at the specified resolution, sample aspectratio and frame rate. In a number of embodiments, if the bitrate doesnot have a corresponding smallest positive difference, there is nocorresponding encoding bitrate and the resolution and frame ratecombination for the video data is not allowed. In other embodiments, ifmore than one bitrate choice is available for the same MAMBPS, then allof the corresponding bitrates are selected for encoding of thealternative video stream at the specified resolution, sample aspectratio and frame rate.

In the event that the set of maximum bitrates changes in response tochanges in the maximum data rates experienced by the playback deviceduring the streaming of the video data, the maximum bitrates at whichthe alternative streams are encoded will change accordingly. An exampleof a set of video encoding bitrates and minimum adjusted macroblocks persecond which could be utilized for adaptive bitrate streaming ofalternative streams of video encoded at resolution and sample aspectratio combinations and maximum bitrates corresponding to the displayaspect ratios and network connection maximum data rates of playbackdevices receiving the streams in accordance with embodiments of theinvention is illustrated in FIG. 6. As the maximum data ratesexperienced by the playback device vary during the streaming of videodata, alternative streams of video data will be selected. Typically, thealternative streams of video include at least one alternative stream ofvideo data that has a maximum bitrate corresponding to the maximum datarate that is likely to be experienced by the playback device. Forexample, an adaptive streaming system may be streaming multimediacontent to a playback device with video data at a resolution of1920×1080 at 30 frames per second. This video data may initially have anideally determined encoded bitrate of 8969 Kbps with calculated adjustedmacroblocks per second of 243000. Referring to FIG. 6 and FIG. 5, thecolumn labeled Profile 1 indicates that a group of playback devices havenetwork connections with an anticipated maximum bitrate of 8400 Kbpswould have corresponding adjusted macroblocks per second of 217000.Therefore, the video stream at 1920×1080 would have been encoded at 8400Kbps instead of 8969 Kbps, and selected as the streamed video stream.During streaming, a playback device that typically experiences a maximumbitrate of 8400 Kbps may suffer some network congestion, reducing themaximum available bitrate to 2800 Kbps. In accordance with the aboveprocess, the adaptive bitrate streaming system will adjust the videodata stream to be streamed by selecting an alternative stream having amaximum bitrate that is less than the data rate of the playback device'snetwork connection. As seen in FIG. 6, the nearest bitrate is 2400,resulting in the adaptive streaming system switching to an alternativestream of video data having a minimum adjusted macroblocks per second of102000 according to the column labeled Example Profile 1. For example, astream of video data at a resolution of 1280×720 at 30 frames per secondhas a calculated adjusted macroblocks per second of 108000; therefore,the adaptive bitrate streaming system will switch to this alternativestream of video data to ensure smooth delivery and playback at thereduced network data rate. Additionally, the video data at resolution of1280×720 may have been encoded according to the bitrate value of 2400Kbps, as indicated by the table in FIG. 6. For a system that is based onthe streaming characteristics of the column labeled Encode Profile, thevideo data at resolution of 1280×720 may have been encoded according tothe bitrate values of 2400 and 1750 Kbps, because the closest minimumadjusted macroblocks per second value that is less than 108000 is 60000,and this corresponds to the two bitrates which have been specified inFIG. 5. It should be noted, however, that the alternative streamselected will be the stream with the smallest positive differencebetween the calculated adjusted macroblocks per second of the stream andthe adjusted macroblocks per second of the maximum bitrate correspondingto the available data rate.

Although a specific process is described above, there are a variety ofmethods to determine the resolution and sample aspect ratios ofalternative streams of video and the maximum bitrates at which to encodeeach of the alternative streams of video in accordance with embodimentsof the invention. Systems and methods for determining adjustment factorsfor calculating the bitrate threshold beyond which the video quality ofan alternative stream encoded at specific frame rate no longerappreciably improves in accordance with embodiments of the invention arediscussed below.

The Adjustment Process

Given video data at a particular frame rate, adjustments factors can beutilized when determining bitrate thresholds for video streams at lowerframe-rates due to a quality normalization process between lower andhigher frame rates. Frames of video data for content with lower framerates experience a larger time gap between frames; as a result they mayexperience larger motion between objects between frames than those of ahigher frame-rate video sequence. Additionally, due to the non-linearnature of motion, objects may experience a higher degree of predictionerror due to the larger potential time gap between frames in the motionestimation process that is common to many video compression standardswhich may be utilized to encode video data in accordance withembodiments of the invention. In many video compression standards, thelarger motion between objects may ultimately necessitate the allocationof more bits to the encoding of inter-frames in a lower frame ratesequence. Besides the inter-frames, it is also possible that a largerpercentage of intra-frames are present in lower frame rate content.Other factors may also involve an adjustment to the linear calculationof AMBPS. A generalized process for determining an adjustment factor inaccordance with embodiments of the invention is illustrated in FIG. 3.The process 300 may commence by creating (310) source content, such asvideo data, with varying frame rates. In a number of embodiments, thesource content has been previously created. The adjustment factors areinitialized (312) to 1. The encoding bitrate of the source content isdetermined (314) utilizing the frame rate and resolution of the sourcecontent, which may be utilized in a formula which provides an estimatefor the encoding bitrate. The encoding bitrate is then scaled (316) bythe adjustment factor. The content is then encoded (318). Once thecontent is encoded, the encoded content is analyzed (320). In severalembodiments, the analysis (320) is an objective quality analysis. In anumber of embodiments, the analysis (320) is a subjective qualityanalysis. After the content is analyzed, the quality of the encodedcontent at the maximum frame rate is compared (322) to the quality ofthe encoded content at the minimum frame rate. A comparison (324) isthen made. If the quality of the encoded content at the minimum framerate is lower than the quality of the encoded content at the maximumframe rate, the adjustment factor is increased (326) and the processbegins anew starting with scaling (316) the encoding bitrate. In someembodiments, the adjustment factor may be decreased if the quality ofthe encoded content at the minimum frame rate is higher than the qualityof the encoded content at the maximum frame rate. If the quality is notdifferent, the adjustment factor is saved (328) for the lower framerates.

In many embodiments of the invention, the process 300 may be performedfor a variety of types of source content, where the adjustment factor iscalculated as an average of all the encoding of the source content. Inaddition, alternative processes can be utilized to calculate adjustmentfactors for the purpose of determining the maximum bitrates at which toencode specific pieces of content based upon the resolution, and framerate of the encoded content.

Although the present invention has been described in certain specificaspects, many additional modifications and variations would be apparentto those skilled in the art. It is therefore to be understood that thepresent invention may be practiced otherwise than specificallydescribed, including playback devices where the set of streamingswitching conditions utilized by the playback device are continuouslychanging, without departing from the scope and spirit of the presentinvention. Thus, embodiments of the present invention should beconsidered in all respects as illustrative and not restrictive.Accordingly, the scope of the invention should be determined not by theembodiments illustrated, but by the appended claims and theirequivalents.

What is claimed is:
 1. A source encoder configured to encode a sourcevideo stream as a plurality of alternative streams of video for playbackon a playback device, comprising: a processor configured by an encodingapplication to: receive multimedia content, where the multimedia contentcomprises source video data having a primary resolution, a primarysample aspect ratio, and a primary frame rate; and encode the sourcevideo data as a set of alternative streams of video, where: theresolution and sample aspect ratio of at least one of the alternativestreams of video are selected to have an aspect ratio that is the sameas a predetermined display aspect ratio; and at least one of thealternative streams is encoded at a maximum bitrate corresponding to apredetermined network connection maximum data rate.